Prolonged extracorporeal circulation (ECC) using a pump and membrane oxygenator to support heart and lung function is being studied in sheep. The physiologic and hematologic responses to this type of organ substitution are being studied in detail, particularly coagulation, control of coagulation, and platelet function changes. Current studies include: Measurement of oxygenator performance during ECC, measuring platelet disappearance during ECC, application of ECC to lung transplantation and other types of lung damage, and study of patient population to select patients who might benefit from ECC.